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help...losing fish

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First a little background, I have a 220g in wall tank which I just finished a huge makeover. Tank has been running for 3-4 years . Was stocked with 3 sunfish 2 bluegill and a channel cat. I renamed these fish and redecorated the tank and re-stocked . Current stock includes ; 12 neon tetras,6 juvenile Dennison barbs,8 juvenile rainbows( 4 Aussies 2 turquoise and 2 bosemani)6 albino corys and 9 glolite tetras.
I started losing neons about one every other day about a week ago. And today I found one of my dennisons dead...
I have been changing water (30-40% ) biweekly. Current water parameters are :
Ammonia: 0ppm

Nitrite: 0ppm

Nitrate:2.5-5 ppm

PH : 8.2-8.4

I dunno if the high pH is new as I never test for pH until today. I thought ,at first , I just got a bad batch of neons ( first group still doing fine second group came from a different supplier ) . I have well water so I don't normally add anything to water from the tap .

I just tested my tap water and pH straight from the tap is 7.6-7.8.
I am currently letting some water sit and will test again in a couple hours.

I am at a loss here . And am not sure what to do . If tap water is that far off from tank will a big water change change the pH enough to stress these fish ? Is the pH being high even the issue? None of the fish appear to be stressed all are eating well and no signs of a problem .....

Sorry to hear of your loss man, I wouldn't see your pH is too high, the only thing I could think of is the pH swing but your water changes aren't so large that will cause a drastic shift. The next thing that comes to mind is the temperature change of the new water vs that of in the tank, temperature shock has been known to kill fish.

These losses didn't happen just after wc's . And I always measure temp of tap water going into the tank and adjust it to within a degree or two of tank water.... and I don't think a small temp shift is an issue as fish naturally are subjected to temp shift every time it rains....that being said I still try to add water at or near tank temp....
So my high pH is not so high as to cause fish to die? Any ideas?

From what I've learned about neons, most of them are wild caught and undergo a great deal of stress during shipping. They don't seem to be the toughest fish in the world. This stress during transport kills a lot of them, and weakens others so they die later.

Don't know anything about Denison barbs. But if only one has died and the others are all looking well, it could simply be that the one didn't acclimate as well as the others and failed to adjust to its new environment.

Sometimes, no matter how well you try to acclimate new fish, one or two still won't make it. It could simply have been a weaker specimen to begin with.

It sounds like you're doing everything right, and your params are good in a stable tank.

Just one question: When you do WCs, do you also vacuum your substrate and clean your filter(s) when they become clogged and their flow diminishes?

Is there any aggression among your fish? Could one or more be picking on the others?

Even under great conditons, fish can die, and that makes me wonder how old your denison barbs were when you purchased them? What is their normal lifespan? If you got an aged fish, its death may have been natural.

Sorry about the losses. It can be very frustrating not knowing the causes.

When I do my WC's I do vac the gravel . As far as filter cleaning I only clean the filter maybe once A year.....I am running a homemade 55g sump . I do clean the pre- filters regularly but I have found no need the clean the filter...

And yes it is frustrating , but I am feeling better now ...I may just watch and see how it goes . .

I did test my tap water and after sitting the pH was really close to the tank . So I will do my regular WC today .

I do really appreciate all the input guys . Hopefully its just a fluke.

As I said before I don't normally test the pH but I think I will now ...lol just to make sure it is stable ...

On kind of a side note I have been considering plumbing a water line to my tank to make WC easier . I am also considering putting a drinking water filter on this line . Good idea or not? I was thinking about one of the "whole house " style filters with a replaceable micron cartridge . Will that affect the pH ?